The distance traveled can be obtained from the area of the time-velocity graph. As we know when the train passes the post it will travel 100m in 10s. In the graph this region is a trapezoid and its area will be 100.

Area of trapezoid `= (11+V)/2xx10`

`(11+V)/2xx10 = 100`

`V = 9`

So the velocity of train at the start of post is 9m/s.

Using gradient of the graph we can say;

`V/T = 11/(T+10)`

`9/T = 11/(T+10)`

`T = 45s`

So the front of train will pass B after 45 seconds it started travel and with a velocity of 9m/s.